When the efficiency of communication in a parallel computer is increased by optimization of a coupling topology (in other words, a network topology) of servers and switches in the parallel computer, the throughput of parallel distributed processing performed by the parallel computer may be enhanced. Also, if it is possible to couple a large number of servers with a small number of switches by optimization of the network topology in a parallel computer, the construction cost of the parallel computer may be reduced.
A document discloses a network topology called a Latin square fat-tree. The Latin square fat-tree has the characteristics that between any two different Leaf switches, there exists a path that goes through Spine switches. When a Latin square fat-tree is used, it is possible to couple many servers with less number of switches, compared with a typical two-stage fat-tree.
Meanwhile, all-to-all communication is collective communication in which each of servers performs communication with all other servers, and thus communication volume is large and route conflict is likely to occur as compared with other collective communications such as all-reduce communication. Here, the route conflict means that multiple packets are transmitted at the same time over a route in the same direction. In a system which adopts a Latin square fat-tree (hereinafter, referred to as a Latin square fat-tree system), multiple jobs are executed concurrently and all-to-all communication may be performed in each of the multiple jobs. In such a situation, no technique in related art suppresses an occurrence of path conflict. Related technique is disclosed in M. Valerio, L. E. Moser and P. M. Melliar-Smith, “Recursively Scalable Fat-Trees as Interconnection Networks”, IEEE 13th Annual International Phoenix Conference on Computers and Communications, 1994.